This invention relates generally to methods and apparatus for coating the internal surfaces of tubular structures. More particularly, this invention relates to methods and apparatus for coating in a very controlled and precise manner the internal surfaces of very small diameter tubular structures such as, for example, vascular grafts. The configuration of the tube of interest may be circular in cross section or it may be somewhat elliptical if somewhat flexible, depending upon how the structure is formed in the first place.
One particular problem is the fact that while many grafts are solid, some are formed with a porous wall and the controlled application of the invention here is utilized to accommodate these variations.
In its broadest sense, the invention here includes the coating of the internal surfaces of tubular conduit-type structures since the structures to be coated are substantially longer than the diameter thereof and it is necessary to provide a precise consistent coating on the internal surface of the entire length of the tubular conduit. For example, tubular members, such as vascular grafts and common tubing used in medical applications, may have substantial length and require uniformity throughout the length thereof on the internal surfaces thereof.
Other tubular structures which may be coated internally with the methods and apparatus herein include textile circular braid, metallic or ceramic tubular substrates and other tubes which require internal coatings. Materials to impart biocompatibility, internal lubricity, optical viability, corrosion resistance, hydrophobic and hydrophilic interfaces and abrasion resistance are all applications appropriate for the methods and apparatus herein. While the invention here is not limited to specific coating materials, it is preferable that polymeric coatings are utilized for the various applications herein.
As mentioned previously above, the coating of the internal surfaces of vascular grafts is one particular application of the method and apparatus of the invention here. As is well known by practitioners in-the-art, vascular grafts come in a variety of configurations and compositions and it is important to be able to accommodate these various configurations and compositions and still coat the internal surface with a coating consistent and appropriate for the application of the graft in place in the human body. For example, grafts come with external reinforcement wrappings of small bonded rod stock and with convolutions in the walls thereof. Nevertheless, these grafts require certain coating applications internally for the use to which they are to be applied. The coating applications, in accordance with the methods and apparatus here, must be controlled to provide for the ultimate requirements of the device being coated for subsequent use.
In considering generally the conditions for carrying out the invention herein, it should be noted that the applicator for the invention is comprised, preferably, of a sintered brass material which provides the appropriate interstices for "applying" the polymer coating material against the internal surface of the graft. Other materials which may be utilized for the applicator include ceramic materials, zinc/nickel alloys and stainless steel. The material will be selected for the specific application and the chemical content of the coating material. Obviously, if the chemical content is such as to react with the material of the applicator head, it would deteriorate the head.
The arrangement herein is such that the tubular structure is mounted to hold the ends precisely in place and maintain the internal surface available for passage of the spray head therethrough. Subsequently, appropriate apparatus is started for moving the spray head longitudinally through the length of the material to be coated in a controlled manner not only with respect to the speed of movement, but also with respect to the degree of feeding of the coating material and the particular nature of the coating material. Obviously, as will be understood by practitioners-in-the-art, the viscosity of the coating material will be a factor in the speed by which the spray head is moved through the tubular substrate to be coated, and also the pressure under which the material is to be applied.
As a particular feature of the invention herein, in applications where the material for coating is a polymeric material with a solvent, provision is made for a simultaneous spraying with a water head against the already coated surface which water head moves through the internal surface of the material to be coated following the polymer spray head so that the solvent is washed from the polymer material immediately after its application to set the polymer coating and avoid any adherence between opposed surfaces of the internal tubular structure.
One of the problems of coating elongated tubular structures of the kind to which this invention is directed is the fact that there is a great longitudinal length compared to the length of the applicator or coating head for applying the coating. For this reason, the applicator head must pass through the length of the tube to be coated so that the internal surface thereof is evenly coated throughout the length. Also, for this reason, the tubular material to be coated must be held in place at each end thereof for maintaining a stable internal tubular surface for movement of the coating head. Moreover, provision is made selectively for the devices for holding each end of the elongated tube to be rotatable. The material to be coated may be rotated versus the applicator head for, again, evenly distributing the coating material on the internal surface of the tube being coated.
In this respect, generally prior art arrangements for coating the internal surface of structures require a spinning head for even application of a coating material to the internal surface of a hollow container, for example. Representative such devices are described and claimed in U.S. Pat. No. 4,233,932 which issued Nov. 18, 1980.
As purely illustrative of apparatus which may be used for carrying out this invention, one may note the attached drawings in which a representative device is illustrated for coating the internal surface of tubular structures, and particularly vascular grafts, including an arrangement for holding the graft in an appropriate orientation for coating the internal surface thereof as well as arrangements for removing immediately, the solvent content of the polymer coating material applied to the internal surface of the graft.
Other objects and advantages of this invention will be apparent from the following description, the accompanying drawings and the appended claims.